1. Technical Field
The present invention relates to a method and apparatus for cathodically protecting reinforced concrete structures, such as the decks or substructures of bridges, wharfs and parking garages. The present invention especially relates to a cathodic protection apparatus which can be utilized in a variety of applications, e.g., from patching old concrete to installation in new construction.
2. Description of the Prior Art
Steel corrosion, in steel reinforced concrete structures, is the result of electrical current flowing from one point of the steel reinforcement to another. Such corrosion is enhanced by moisture and salt contamination of the concrete. Conventional cathodic protection applies an external direct current to the steel reinforcement from a current distribution anode which is in intimate contact with the concrete surface. The current from the distribution anode counteracts the corrosive current.
A technical bulletin captioned "Raychem Ferex 200 Cathodic Protection for Reinforced Concrete Structures" discloses a cathodic protection system for reinforced concrete structures. The system comprises flat anode strips and plastic channels by which the anode strips are attached to the underside of a concrete structure. The anode strips comprise an anode and a gel-like material which provides contact between the anode and the concrete structure. The gel-like material also conforms to irregularities in the concrete surface. The system is installed by preparing the surface of the concrete, attaching the anode strips and support channels to the prepared surface, wiring the system together, and then connecting the system to a power source. The anodes are in the form of an anode wire made of a conductive polymer electrode material coated onto copper conductors. The conductive polymer serves as an active anode material and also shields the copper conductors from chemical attack.
U.S. Pat. No. 4,812,212 discloses an anode structure for cathodic protection of the reinforcing members of reinforced concrete. The anode structure comprises an electrically conductive graphite tape. The tape is connected to a direct current power source. An electrically insulating backing is disposed between the tape and the surface of the reinforced concrete. The anode also has a conductive mastic or polymer which covers the graphite tape and which extends beyond the edges of the tape onto the concrete surface. The conductive mastic or polymer distributes a cathodic protection current from the graphite tape to the reinforced concrete.
U.S. Pat. No. 4,496,444 discloses an anode for cathodic protection of a metallic structure, such as a steel pipe, subject to corrosion. The anode comprises a strip or band of sacrificial anodic material. The strip or band has a pressure sensitive adhesive layer which permits the strip or band to be adhesively secured directly to the metallic structure. The adhesive layer is electrically conductive, and has a protective covering which permits the anode to be rolled up without adhesion between adjacent windings of the anode. Examples of adhesives disclosed in the patent are acrylic glues or vinyl glues.
U S. Pat. No. 4,506,485 discloses a system for cathodic protection of reinforced concrete structures. The system comprises a current distributing anode coating of zinc metal which is flame-sprayed onto at least a part of the exposed concrete surface. The zinc anode coating is connected with the reinforcing steel through a power source by which current flow is induced from the coating to the reinforcing steel. By flamespraying the metal onto the concrete, a coating is obtained which, in contrast to a metal paint, is free of a binder, and thus is more conductive. The flamesprayed metal anode coating more effectively distributes the cathodic protective current to the reinforced concrete structure than a metal paint.
In addition to strips or tapes, or sprayed systems of sacrificial metal applied to the surface of an object to be protected, it has also been known to cut channels into concrete and to place a sacrificial metal anode in the channel. Danish Patent No. 104,493 discloses cutting channels into concrete near steel reinforcement and then placing magnesium anodes into the channel. A resilient, preferably foam, material can be placed in the channel with the anode. This material can be compressed by the expansive corrosion products resulting from the corrosion of the sacrificial anode.